Pores, nuclear

Expoitins are transport receptors at the nuclear pore complex needed for the selective export of proteins from the nucleus into the cytoplasm. They recognize nuclear export signal sequences of cargo proteins. 

The nuclear pore complex, located in the nuclear envelope, contains more than 50 proteins. It allows diffusion of small proteins between cytoplasm and nucleoplasm. Larger molecules (>50kD) are selectively transported by an energy-dependent mechanism. 

Rout, M. P., Aitchinson, J. D., Suprapto, A., Hjertaas, K., Zhao, Y., and Chait, B. T. (2000). The yeast nuclear pore complex composition, architecture, and transport mechanism. J. Cell Biol. 148, 635-651. 

Connective tissues, collagen and hydrogels of nuclear pore proteins... 

After synthesis, the mRNA exits the nucleus through a nuclear pore and proceeds to the ribosome for translation into protein. Competing with export and translation is the process of message degradation by cellular ribonucleases. The competition between degradation and translation provides another mechanism to regulate the levels of individual messages. 

FIGURE 1-5 Detail of the nuclear envelope showing a nuclear pore (single arrow) and the outer leaflet connected to the smooth endoplasmic reticulum (ER) (double arrows). Two cisternae of the rough ER with associated ribosomes are also present. X80,000. 

Ran (the Ras-related nuclear protein) is the major regulator of nucleo-cytoplas-mic transport [134] across the nuclear pore complex (NPC). Like other small Ras-like GTP-binding proteins, it switches between a GTP- and a GDP-bound form by GTP-hydrolysis and nucleotide exchange [135]. In contrast to its relatives, Ran does not undergo posttranslational modification. 

The recycling process of Ran between its GDP and GTP complexed state is supported by another class of Ran-binding proteins, which support GTP-hydro-lysis by RanGAP and are either soluble proteins [ 143] or part of the nuclear pore complex [144]. 

Bustamante JO, Liepers A, Prendergast RA, Hanover JA, Oberliethner H. Patch clamp and atomic force microscopy demonstrate TATA-binding protein (TBP) interactions with the nuclear pore complex. JMembrane Biol 1995 146 X263-X272. 

Harris N. Nuclear pore distribution and relation to adjacent cytoplasmic organelles in cotyledon cells of developing Vida faba. Planta 1978 141 121-128. 

The nuclear envelope is composed of the nuclear membranes (inner and outer), the nuclear lamina, and the nuclear pore complexes. The inner and outer nuclear membranes are connected at the nuclear pore sites and enclose a flattened sac... 

Nuclear pore complex protein nu Accession number swissprot P52948... 

The nucleus is surrounded by the nuclear envelope, which takes on a lumenal structure connected to the endoplasmic reticulum. The transport of proteins into (and out of) the nucleus occurs through the nuclear pore complex (NPC), a large complex composed of more than 100 different proteins (Talcott and Moore, 1999). Because NPC forms an aqueous pore across the two membranes, small proteins less than 9 nm in diameter can pass through it simply by diffusion. However, most of the transports of both proteins and RNAs are mediated by an active transport mechanism. It is now clear that there is heavy traffic through the NPC in both directions. Proteins are not only imported into the nucleus but also actively exported from it as well. There are many reasons for nuclear export. One reason is to send some shuttle proteins back after their import another is for some viral proteins to export their replicated genomes outside the nucleus. 

Smith, H., and Raikhel, N. (1999). Protein targeting to the nuclear pore. What can we learn from plants Plant Physiol. 119, 1157-1163. 

Talcott, B., and Moore, M. (1999). Getting across the nuclear pore complex. Trends Cell Biol. 9, 312-318. 

Nuclear Envelope The membrane system of the cell nucleus that surrounds the nucleoplasm. It consists of two concentric membranes separated by the perinuclear space. The structures of the envelope where it opens to the cytoplasm are called the nuclear pores (nudear pore). [NIH]... 

Nuclear Pore An opening through the nudear envelope formed by the nudear pore complex which transports nuclear proteins or RNA into or out of the cell nucleus and which, under some conditions, acts as an ion channel. [NIH]... 

Mahajan, R., Delphin, C., Guan, T., Geeace, L., and Melchior, F. A small ubiquitin-related polypeptide involved in targeting RanGAPl to nuclear pore complex protein RanBP2, Cell, 1997, 88, 97-107. 

Matunis, M. j., Coutavas, E., and Blobel, G., a novel ubiquitin-like modification modulates the partitioning of the Ran-GTPase-activating protein RanGAPl between the cytosol and the nuclear pore complex,/. Cell. Biol., 1996, 135, 1457. 

Melchior, F., Schergaut, M., and Pichler, a., SUMO ligases, isopeptidases and nuclear pores. 

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